[net,1/2] tun: read vnet_hdr_sz once
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Message ID 20170203232049.38982-2-willemdebruijn.kernel@gmail.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Willem de Bruijn Feb. 3, 2017, 11:20 p.m. UTC
From: Willem de Bruijn <willemb@google.com>

When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
Data length is verified to be greater than or equal to expected header
length tun->vnet_hdr_sz before copying.

Read this value once and cache locally, as it can be updated between
the test and use (TOCTOU).

Signed-off-by: Willem de Bruijn <willemb@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
CC: Eric Dumazet <edumazet@google.com>
---
 drivers/net/tun.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Comments

Eric Dumazet Feb. 3, 2017, 11:27 p.m. UTC | #1
On Fri, 2017-02-03 at 18:20 -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
> Data length is verified to be greater than or equal to expected header
> length tun->vnet_hdr_sz before copying.
> 
> Read this value once and cache locally, as it can be updated between
> the test and use (TOCTOU).
> 
> Signed-off-by: Willem de Bruijn <willemb@google.com>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> CC: Eric Dumazet <edumazet@google.com>
> ---

Acked-by: Eric Dumazet <edumazet@google.com>

Patch
diff mbox

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2cd10b26b650..bfabe180053e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1170,9 +1170,11 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	}
 
 	if (tun->flags & IFF_VNET_HDR) {
-		if (len < tun->vnet_hdr_sz)
+		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
+
+		if (len < vnet_hdr_sz)
 			return -EINVAL;
-		len -= tun->vnet_hdr_sz;
+		len -= vnet_hdr_sz;
 
 		if (!copy_from_iter_full(&gso, sizeof(gso), from))
 			return -EFAULT;
@@ -1183,7 +1185,7 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
 		if (tun16_to_cpu(tun, gso.hdr_len) > len)
 			return -EINVAL;
-		iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso));
+		iov_iter_advance(from, vnet_hdr_sz - sizeof(gso));
 	}
 
 	if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
@@ -1335,7 +1337,7 @@  static ssize_t tun_put_user(struct tun_struct *tun,
 		vlan_hlen = VLAN_HLEN;
 
 	if (tun->flags & IFF_VNET_HDR)
-		vnet_hdr_sz = tun->vnet_hdr_sz;
+		vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
 
 	total = skb->len + vlan_hlen + vnet_hdr_sz;